It's a big week for "Call of Duty 4." And it's a big week for songs that play when video game credits roll.

So shouldn't it be a big week for Mark Grigsby?

Don't know him? You might be more familiar with him than you realize. Grigsby was the lead animator on "Call of Duty 4," a game that sold 7 million copies in 2007, according to publisher Activision. One of its characters, Staff Sergeant Griggs, is voiced by Grigsby. And the song that plays when the credits roll ... Grigsby rapped that.

Yes, it's a big week for "Call of Duty 4." The game was a sales blockbuster and a critical hit and is being re-released in a "Game of the Year" special edition. And this week is historic for end-of-game songs because the list of downloadable bonus tracks for MTV's music game, "Rock Band," is being fattened by the addition of the end-credits hit from last year's "Portal": Jonathan Coulton's "Still Alive." That's right: A video game song was so compelling that it's being released as a song for people to perform together with drums, guitar and mic. "Still Alive," a cultural phenomenon since it was first heard, is just that big with gamers.

Despite all this, there hasn't been much discussion about Grigsby's "Call of Duty 4" rap. Surely millions of people have heard his song. But what's the story behind it?

Before he got a career in gaming, Grigsby had other dreams and hobbies. One of them was rapping. In 1997, in Dallas, he and two friends were in a group called Village of the Damned. He went by Grigsby/Dirtymouth. His partners were Goodson/Son-Ra and Mr. Mysterious/ Da Sauce. They got a little play on their local radio station, KNON-FM 89.3, with a song called "Sill Hollerin.'" "I started rapping way back in the day," Grigsby told GameFile recently in Las Vegas, right after "Call of Duty" had taken top honors at a gaming conference. "I had a crew and everything. But my passion was animation, so I had to leave my crew and do my thing."

Grigsby got into video games. Three years ago he joined Infinity Ward, working with the team there during the final months of making "Call of Duty 2." Then he and the rest of the team started on the fourth installment ("Call of Duty 3" would be made at a different development studio.)

He said he still rapped "here and there" but wasn't serious about it. His colleagues at Infinity Ward knew about his talent, though, and suggested he help come up with a song for the game's ending credits. But if he had his way, he wouldn't have been the one rapping while the names scrolled by. He suggested a favorite Brooklyn rapper. "They were looking for inspirational songs for the end credits," he said. "I definitely love Boot Camp Clik and love Sean Price, so I'm like, 'Let's get a Sean Price.' " This is the kind of thing a game developer can decide to do: hire a favorite actor or musician. But it's helpful for others on the team to agree. Grigsby found that Price wasn't who his colleagues were looking for. They wanted him. "We wanted something more personal and everybody wanted me to do it. So I did the end-song credit."

The Sean Price song he had in mind for the end got tucked into a midgame level. It plays briefly at the conclusion of a stage called Charlie Don't Surf. That level features Grigsby's character as part of a modern military squad in action in a fictional Middle Eastern country. "At the end of that level, there's a broadcast going on with one of the bad guys and one of my sergeants says, 'Griggs, turn it off,' " he recalled. "I go, 'Roger that. I got something better anyway.' So I go over and turn the broadcast off and I put Sean Price on. And then he plays for 10 seconds." Grigsby wishes it went longer but is still proud of the inclusion: "One of my heroes of hip-hop in the game."

Grigsby's rap isn't that deep. It repeats a lot. And some of its elements would mystify people who haven't played the game. In fact, some elements probably mystify people who have played the game. It begins with a sample of a man saying a little something about the game, wrapping his speech with, "Variety is the next big thing for us. We're going deep and we're going hard." That was an ad lib by an Infinity Ward developer who was giving a presentation at Microsoft's E3 press conference last year. The provocative line became an office motto/joke, winding up on freebie T-shirts that were distributed to the press and becoming part of Grigsby's hook.

The second thing people listening to the song hear is a gravelly voice saying, "The weak man better be careful not to soil himself when he plays this game." That's the game's military adviser. And then Grigsby starts rapping, name-checking his own character, calling out his character's serial number, "678452056," and offering verses, including M-rated lines such as: "Sgt Griggs reporting for duty/ Some say this belong in a movie/ But this the third installment of Infinity Ward sh--/ Don't soil your drawers, because it's deep and it's hard, bi---."

Grigsby said the song is a send-up, a tribute to his team and a celebration of that press-conference ad lib that got the whole team rolling. It became their catchphrase — kind of a joke, kind of a rallying cry. "Basically the whole song tells the story of what happens in the game and at the same time praising Infinity Ward."

The song does not signal a return for Grigsby to his Dallas days. In an e-mail, he mentioned he's "not pursuing a career in music." He added, "It's just something I do." He's keeping his day job.